A simple seismograph recording on a plate without time marks.
instrument for detecting earthquakes
• (n.) A seismometer.
(from the article `seismograph`) An early seismic instrument called the seismoscope made no time record of ground oscillations but simply indicated that shaking had occurred. A ...
Seis'mo·scope noun [ Greek ......... an earthquake + -scope .] (Physics) A seismometer. 
seismoscope, seismoscopic A simple form of seismometer; a contrivance for detecting or indicating the occurrence of an earthquake shock, sometimes also indicating (without measuring) the intensity or direction of the earthquake waves.
An instrument that registers the occurrence of an earthquake, but not the time.